The term "masterbatch" describes plastic granules which contain high concentrates of colour pigments or additives. Masterbatch contains a higher percentage of pigment or additive than the finished product. Masterbatch is made up of raw polymers which are then dyed or otherwise processed. Polymer-based masterbatch in granulate form guarantees a higher degree of process security than pastes, powder or liquid substances and drastically produces less pollution or contamination.

One explanation for the term "masterbatch" comes from the general term used in the production of rubber. Historically, only a master craftsman was allowed to manufacture and mix the high concentrated batches (hence masterbatch).

There are basically three groups of masterbatch: colour masterbatch (monopigment or tailor-made) which is used to dye plastic goods, additive masterbatch which determines specific properties of the end products (i.e. UV stabilisers, flame protection, anti-static or anti-block) and finally combination masterbatch with both dyes and additives. Masterbatch is generally concentrated in a pigment and/or additive ratio of 40% ± 10%.

With help of an extruder (normally twin screw), polymers, pigments and/or additives are blended into a homogenous mixture. This is achieved using a "pre-mix" or "split feed" process.

During the pre-mix process, a pre-mixture of polymer, pigment/additive and eventually dispersion means are brought together in the main inlet area. This "pre-mix" is placed into mixers in batches. The melting, wetting, homogenisation and dispersing processes takes place in the extruder. A volumetric doser is sufficient when using the "pre-mix" process because the recipe elements are exactly weighed and matched in a separate mixer.

During the "spit feed" process, a twin screw extruder is outfitted with a main and side inlet on which a side feeding is installed so that pigment/additive and eventually dispersion means can flow downstream into the already-plasticised polymer and then homogeneously blended. To achieve a consistent recipe mixture, this process must use a loss-in-weight dosing unit at the main and side inlets.

Masterbatch melt in both of the above mentioned processes solidifies after exiting the nozzle by strand, water-ring or underwater pelletising.

The granules are generally filled directly into bags. In a further procedure, monopigment or additive masterbatch is drawn into plastics processing machines such as injection or blow moulding, sheet or cable extruders for dyeing or finishing the end products.